Overvoltage arrester having stacked arrays of arc gap and grading resistor units



3,366,831 705* ARC LAPFLE Jan. 30, 1968 J,

ovmvommz ARRESTER HAVING STACKED ARRAYS GAP AND GRADING RESISTOR- UNITSFiled April 14, 1965 Inventor:

Jan. 30, 1968 J, APP| E 3,366,831

OVERVOLTAGE. ARRESTER HAVING STACKED ARRAYS OF ARC GAP AND GRADINGRESISTOR UNITS Filed April 14, 1965 5 Shaw-Sheet 2 Fig.3

5 5d 5f 5c 5 6a In van (or:

Jan. 30, 1968 .LAPPLE 3,366,831

OVERV-OLTAGE ARRES HAVING STACKED ARRAYS OF ARC GAP AND GRADING RESISTORUNITS Filed April l4, 1965 5 Sheets-Sheet :2

1 /nvenibr:

v y W United States Patent Ofiice 3,366,83l Patented Jan. 30, 19683,366,831 OVERVOLTAGE ARRESTER HAVING STACKED ARRAYS F ARC GAP ANDGRADING RE- SlSTOlR UNITS Johannes Liipple, Berlin, Germany, assignor toSiemens- Schuckertwerke Aktiengesellschaft, Berlin-Siemensstadt,Germany, a corporation of Germany Filed Apr. 14, 1965, Ser. No. 448,024Claims priority, application Germany, Apr. 17, 1964, S 90,594 Claims.(Cl. 315-46) ABSTRACT OF THE DISCLOSURE An overvoltage arrestercomprises a mu1tilevel stack of sections with insulating plates betweenadjacent ones of the sections. The section of each level has a spark-gapdevice and a discharge resistor mounted in mutually spaced relation in acommon plane. The spark-gap is electrically connected with the resistor.Conductive coatings are provided on the insulating plates in electricalcontact with the spark-gap, the resistor and the electrical connectorbetween the spark-gap and the resistor.

My invention relates to overvoltage surge protection devices. Moreparticularly, it relates to novel overvoltage arresters capable ofhandling very high voltages.

In high voltage systems, such as in polyphase interconnected systems,there is the need for handling external overvoltages caused by lightningand internal overvoltages which are essentially caused by transientswitching phenomena. To handle such high overvoltages, heretofore therehas been required expensive insulation. To decrease the expense of suchinsulation, there have been utilized voltage arrester devices which, asprotective devices against internal overvoltages, have the taskessentially of absorbing the charging energy of the systems capacitancesand of discharging the accompanying long duration currents to ground.

A type of voltage arrester capable of being used where voltages up to1000 kv. are involved which has been effectively utilized to enable agreat saving in insulation is one which comprises a vertical stack oflike sections, each of the sections comprising a spark gap device or agroup of spark gap devices and a plurality of non-linear dischargeresistors, the spark gap device and the discharge resistors for eachsection being suitably physically disposed in a polygonal arrangement onan insulating plate and electrically connected in series. Each sectionof the stack lies on the immediately underlying section. Thecorresponding elements in each section may advantageously berespectively disposed on insulating plates. With such arrangement, theover-all height of the stack may be appreciably reduced. The stack ofsections is suitably housed in a hermetically sealed housing such as anitrogen filled hermetically sealed porcelain housing.

It has been found that high frequency voltage discharges occur in theoperation of such arrester and thereby interfere with the properfunctioning thereof under operating conditions. A salient cause of theproduction of such interfering high frequency voltages is the juxtaposedcontact of the surface of an insulating plate and the conductiveelements of an adjoining section. Since such contacting plate surfaceand the surfaces of the conducting elements are inherently unevenwhereby contact is made only at a few points and the contact surfacesare at a slight distance from each other, voltages which may have amagnitude of kv. may be present in the air gaps between said contactsurfaces. Such voltages lead to the production of undesired anddeleterious corona discharges.

Accordingly, it is an object of this invention to provide a stack-typehigh-voltage surge protection device, whose operation is substantiallyfree of high frequency voltage interference.

To this end, and in accordance with a feature of my invention, I providethe insulating plates in an overvoltage arrester of the above-mentionedstack type with a conductive coating on the surface areas contacted bythe adjacent active arrester components and their metallicinterconnections.

Preferably, and according to more specific features of the invention,there is provided an overvoltage arrester comprising a stack of likesections, each of the sections comprising an insulating plate, aspark-gap structure and a plurality of discharge resistance members oneach plate spaced fromeach other in a polygonal groupmeans forelectrically connecting the spark-gap structure and the resistance inseries arrangement, with the spark-gap structure being electricallydisposed intermediate the resistances, to provide first and second endresistances in each series arrangement, each of the spark-gap structuresand the respective first and second end resistances in the sectionsbeing disposed in vertical registration each insulating plate of asection resting on the adjoining next lower section. An opening isprovided in each plate of one set of alternately occurring insulatingplates to permit the first end resistances to make direct electricalcontact with each other and an opening in each plate of the other set ofalternately occurring plates to permit the second end resistances tomake direct electrical contact with each other. There is furtherprovided an electrically conductive metallic coating in each side of theplate on the areas occupied by the spark-gap structure and theresistances other than the end resistance in direct contact with itsregistered resistance in the adjoining lower section and in a cross areaconnecting the occupied areas.

The foregoing and more specific objects and features of my inventionwill be apparent from, and will be mentioned in the followingdescription of the overvoltage arrester according to the invention shownby way of example in the accompanying drawing, in which:

FIG. 1 is an exploded three dimensional View of an illustrativeembodiment of an arrester constructed in accordance with the principlesof the invention;

FIG. 2 is an exploded perspective View of some of the components of thesame arrester;

FIG. 3 is a sectional view of an assembled arrester according to FIGS. 1and 2;

FIG. 4 is a plan view of an insulating plate structure in a modificationof the embodiment shown in FIG. 1;

FIG. 5 is a view taken along lines VV in FIG. 4 looking in the directionof the arrows with other associated structures depicted in broken line;and

FIG. 6 is a view taken along lines VI-VI in FIG. 4

' looking in the direction of the arrows with structures resting thereondepicted in broken line.

lceierring now to FIG. 1 which shows an exploded three dimensional viewof a few sections of a vertical stack type voltage arrester, eachsection comprises a substantially triangular group of a pair ofnon-linear discharge resistors and a spark gap on an insulating plate.'lhus, in the upper section of the three sections shown in FIG. 1, thespark-gap structure is designated by the numeral 5, the non-lineardischarge resistors are designated by the numerals 4 and 6, and theinsulating plate is designated by the numeral 1. Correspondingly, in themiddle section, the spark-gap structure is designated by the numeral 8,the respective non-linear discharge resisters are respectivelydesignated by the numerals 7 and 9 and the insulating plate isdesignated by the numeral 2. The lower section in FIG. 1 comprises theinsulating plate 3 on which there are disposed in substantiallytriangular array, spark-gap structure 11 and non-linear dischargeresistors and 12.

The spark-gap structures are respectively physically engirdled, asnumerically designated at spark-gap structure 5 in FIG. 2, by annularcontrol resistors in and control capacitors 5b. The resistors 5a andcapacitors 5b are electrically connected in parallel with the sparkgapstructure such as spark-gap structure 5. It is, of course, to berealized that the spark-gap structures need not comprise a unitarystructure but may include a plurality of superposed spark-gap deviceunits. The insulating plates may suitably have a roughly polygonaloutline corresponding to the type of array of circuit elements on eachinsulating plate. Thus, in the embodiment shown in FIG. 1, insulatingplates have a roughly triangular configuration.

In each section, the non-linear discharge resistors such as resistors 43and 6 on insulating plate ll may each be chosen, for example, to handlea voltage of 2.5 kilovolts (kv.) and the spark-gap structure, such asspark-gap structure 5, may be rated for a voltage of 5 kv. The conresponding non-leakage resistors and spark-gap structures in the othersections of the vertical stack are correspondingly chosen to handle likecorresponding voltages. Accordingly, each section in the stack may beconsidered, using the above values, as a unit for 5 kv.

The electrical connections between the elements in each section are ofthe series type. However, the order of series connection is alternatelyreversed in successive sections. Thus, in FIG. l, in the upper section,the series connection order is resistor 4, spark-gap structure 5 andresistor 6; in the intermediate section, the series connection order isresistor 7, spark-gap structure 8 and resistor d; and in the lowersection, the series connection order is resistor it spark-gap structureill and resistor 12. The conductor winding directions in alternatelyoccurring sections are consequently in opposite directions as indicatedby arrows 13, 14 and respectively to provide a noninductive windingarrangement analogous to a bifilar noninductive wiring scheme. No loopareas for introducing inductance effects exist therein.

he corresponding elements in each section are disposed in registration,i.e., resistors d, 9, and 1t), sparkgap structures 5, 8, and 11, andresistors e, 7, and 12 are in respective vertical alignments. Theinsulating plate of a section lies directly on the spark-gap structureand a resistor of the immediately lower section as determined by thenoninductive winding arrangement. Thus, in FIG. 1, insulating plate 1,rests on resistor 9 and spark-gap structure 8. A hole in coextensivewith the size of the surface of resistors 6 and 7 is provided in plate 1to enable resistors 6 and 7 to make direct electrical contact.Correspondingly, insulating plate 2 rests on spark-gap structure 11 andresistor 12 and a hole is provided in plate 2 to enable resistor 9 tomake direct electrical contact with resistor 14). The electricalconnections between the elements in a section, shown in heavy blacklines at 4a and 6:: (FIG. 1), are suitably sheets of. metal which reston the elements as shown in FIG. 2. The stack of sections is enclosed ina hermetically sealed insulating housing, (not shown), suitablyporcelain, in a neutral gas atmosphere such as nitrogen.

Referring to FIG. 2, it will be seen that the spark-gap structure 5 inthis embodiment is composed of two individual spark-gap memberscoaxially adjacent to each other and surrounded by the two controlresistors 5a of which each has the shape of a circular segment. Thecontrol resistors 5a consist of silicon carbide and bonding medium inthe conventional manner. The two control capacitors 5b are likewiseshaped as segments of a circle. They consist. of a ceramic materialhaving a high dielectric constant and are provided with metal coatingson the top and bottom faces respectively. The resistor d also consistsof silicon carbide and bonding medium. It has A a relatively highconductivity in comparison with the control resistors 5a.

The set of components 5, 5a and 511 on the one hand, and the dischargeresistor 6 on the other hand, are connccted with each other on theirrespective top sides by the above-mentioned conductor 6a consisting of asheet of electrically conductive metal having approximately a lemniscateshape. The conductive sheet 6a is in electrical contact engagement withthe top faces of the respective components. The conductor ta on thebottom side of the components has the same shape as the conductive sheet6:! and connects the components in the same manner with the bottom sideof the discharge resistor 4.

FIG. 3 shows a section through components 4a, 5a, 5b and 6a in assembledcondition. Each of the two are gap structures 5 and 5 is bordered by twoinsulating plates 50 respectively. The are electrodes are denoted bySt]. These electrodes are conduct-ively connected with metal plates 5earranged on the outer sides of the insulating plates 50. The device isprovided with sheets 5] of magnetizable material extending parallel toeach other and forming a quenching gap into which the arc occurringbetween the electrodes 5b upon response of the device is driven.

The insulating plates 1, 2 and 3 according to FIG. 1 may consist forexample of epoxide resin with filler substances such as quartz powder.

In the type of voltage arrester as described, the operation is based onthe electromagnetic blow-out principle. A deflecting force, caused by aunilateral magnetic field produced by current acts upon an arc anddrives it away from a sparkover point. The are is thus extended to amultiple of its original length and broken up into a large number ofseparate smaller arcs which are cooled. Since the root of the arc israpidly driven away from the initial sparkover point, the sparlogapelectrode is not subjected to thermal wear at the latter point. Voltagegradation is effected by the non-linear resistors and capacitors. Thecharacteristic electrical values of the resistors and capacitors arechosen such that the magnitude of the sparkover voltage is substantiallyindependent of external stray capacitances and currents over a widefrequency range extending from normal line voltage frequencies to thesteep fronted travelling waves of lightning overvoltages.

Undesirable increases in voltage handled by the arrester due toinductance effects are substantially eliminated by the non-inductivewiring of said arrester.

However, in the arrester in FIG. 1, assuming, for example, a voltagesuch as 5 kv. handled by a section, it is to be noted that twice suchvoltage, namely 10 kv., may build up between two adjacent noncontactingdischarge resistors such as resistors 4 and 9, and '7 and 1.2respectively. The same situation obtains between adjacent spark-gapstructures such as structures 5 and 3, and 8 and 11 respectively. Themetal sheets 4a, 6a which series connect the elements in a section abutboth sides of an insulating plate, i.e., those that connect resistor 4and spark-gap structure 5, and resistor 9 and spark-gap structure 8 abutboth sides of the insulating plate It. However, the metal sheets onlymake contact with insulating plate 1 at a few points. Consequently,spaces result in which discharges can develop to give rise tohigh-frequency interference voltages.

To substantially reduce and minimize such highfrequency interferencevoltages, in accordance with the invention, there is provided aconductive coating in the contact areas of adjacent registered oraligned elements in respective adjacent sections. Such coating maysuitably be provided by the spraying of a metal such as zinc or copperaccording to the Schoop process. Alternatively, the surfaces of theinsulating plates can be provided with a coating of a conductive paintsuch as conductive silver, or a metallized adhesive foil may be used tocover th surfaces of the insulating plates. The point to be noted isthat the metallic coating adheres areally to the surface of the platesat all points where it is provided. The provision of such surfacecontact of metallic coating on the plates produces a uniform potentialwhich is substantially equal to the potential at the area adjoining acircuit element. The elements need not directly abut the surface of theinsulating plate but a sheet of metal can be provided between them andthe surface of the plate, such sheet of metal serving to series connectthe elements in each section.

Thus, referring to FIGS. 4, 5 and 6 the equilaterally triangularlyconfigured plate 1 is the insulating plate of a section such as plate 1in FIG. 1. The opening 1a corresponds to an opening such as 1a in FIG. 1to enable two registered discharge resistors in immediately adjacentsections to make direct contact with each other. Circular areas 21 and22, connected by a linking area 23, coincide in area with the surfaceareas of a discharge resistor and a spark-gap structure which restthereon such as discharge resistor 4 and spark-gap structure 5 shown inFIG. 1. Areas 21 and 22 together with area 23 are coated with a metalcoating 24 (shown in hatching), such as Zinc, such coating beingsuitably deposited by the Schoop spray-deposition process. The undersideof insulating plate 1 is also so metallically coated on its underside inan area coincident with areas 21, 22 and 23. When assembling a sect-ion,an electrically series connecting metallic sheet coinciding inconfiguration with areas 21, 22 and 23, i.e., coating 24 is first placedon coating 24 and then the elements such as a discharge resistor 4 and asparkgap structure 5 are mounted on coated areas 22 and 23 respectively.

In the partially sectional views of FIGS. 5 and 6, the metallic coatingson each side of insulating plate 1 are designated by 24 and 24'respectively. The metallic sheets 25 and 25' on coatings 24 and 24'respectively, series connect the discharge resistor 4 with the spark-gapstructure 5 in the upper sect-ion, and the discharge resistor 9 withspark-gap structure 8 in the next adjoining section. It is thus seenthat no high-frequency voltage interference discharges can occur betweensheets 25 and 25' and the surfaces 24 and 24' of insulating plate 1since such surfaces are always at the same potential.

As shown in FIGS. 4, 5 and 6, areas 21 and 22 and 23 on both surfaces ofthe insulating plate are slightly recessed relative to the surroundingsurface and are partly engirdled, bordered or peripherally enclosed bysubstantially toroidally shaped reinforcing structures 27 integraltherewith. In addition, metallic coatings 24 and 24 preferably terminatein extensions at the sides of the recesses, as shown at points 26, sincethe conditions for forming discharges are particularly favorable at theedges of sheets 25 and 25'.

From the foregoing it is seen that with the providing of metalliccoatings on areas 21, 22 and 23 on both sides of the insulating plate,the conditions for forming highfrequency voltage interference dischargesare substantially eliminated.

It will be obvious to those skilled in the art upon studying thisdisclosure that voltage arresters according to my invention permit of agreat variety of modifications and hence can be given embodiments otherthan those particularly described and illustrated herein withoutdeparting from the essential features of my invention and within thescope of the claims annexed hereto.

I claim: 3

1. In an overvoltage arrester comprising a vertical stack of likesections, each of said sections comprising an insulating plate, aspark-gap structure and a plurality of discharge resistances on eachplate spaced from each other and in polygonal array, means forelectrically connecting said spark-gap structure and said resistances inseries arrangement, with said spark-gap structure being electricallydisposed intermediate said resistances to provide first and second endresistances in each series arrangement, each of said spark-gapstructures and said respective first and second end resistances in saidsections being disposed in alignment, the insulating plate of each ofsaid sections resting on the adjoining next lower section, theimprovement which comprises an opening formed through alternate ones ofsaid insulating plates to permit the first end resistances of alternateadjacent sections to make direct electrical contact with each other, anopening formed through the other alternate ones of said insulatingplates to permit the second end resistances of the other alternateadjacent sections to make direct electrical contact with each other, andan electrically conductive metallic coating on each side of each of saidinsulating plates in the areas occupied by the corresponding spark-gapstructure and the corresponding resistance other than the end resistancein direct contact with the end resistance of the adjoining lower sectionand on a cross area connecting said occupied areas.

2. In an overvoltage arrester as defined in claim 1, wherein saidplurality of discharged resistances comprises two discharge resistancesand wherein the resistances and the spark-gap structure of each sectionare disposed in substantially triangular array.

3. In an overvoltage arrester as defined in claim 2, wherein saidmetallic coating is comprised of zinc.

4. In a overvoltage arrester as defined in claim 2, wherein said meansfor electrically connecting the sparkgap structure and the resistancesin series arrangement in each section com-prises metallic sheetsrespectively having a configuration substantially coincident with theconfiguration of the areas coated with said metal on said areas on bothsurfaces of each of said insulating plates, the spark-gap structure andthe resistance other than the resistance in direct contact with theresistance of the adjacent section being disposed on each of saidmetallic sheets, the sheet on the undersurface of each of saidinsulating plates resting on a spark-gap structure and the resistance inelectrical contact with the resistance of the adjoining lower section.

5. In an overvoltage arrester as defined in claim 4, wherein each ofsaid insulating plates comprises flanged portions partially borderingthe periphery of the coated area, and wherein said metallic coatingsterminate in raised extensions at the junctions of each of said coatedareas with said flanged portions.

References Cited UNITED STATES PATENTS 2,807,751 9/1957 Hilsson -nBIS-36 3,144,583 8/1964 Sorrow 313-23l 3,223,874- 12/1965 Carpenter31323 1 3,248,600 4/1966 Sankey 313-231 JAMES W. LAWRENCE, PrimaryExaminer. STANLEY D. SCHLOSSER, Examiner. R. JUDD, Assistant Examiner.

